The present invention relates to a thermal transfer sheet. More particularly, the present invention relates to a thermal transfer sheet for a thermal transfer system using a sublimable dye, which thermal transfer sheet can provide a sharp full-color image having a satisfactory density and, at the same time, excellent various types of fastness, particularly excellent light fastness.
Various sublimation thermal transfer methods are known in the art, and an advance in the recording method in recent years has enabled fine letters, figures, full-color photographs, and the like to be formed at a high speed by means of a thermal head or the like on a thermal transfer image-receiving sheet comprising a dye-receptive layer formed on a polyester sheet or paper.
In the prior art, the heating time for the thermal transfer by means of a thermal head should be very short. In this case, a sublimable dye and a material, on which an image is to be transferred, are not sufficiently heated, making it impossible to form an image having a satisfactory density. In order to cope with recording at a high speed, a dye having excellent sublimability has been developed. Since, however, this dye generally has a low molecular weight, the dye after transfer to the material, on which an image is to be transferred, lacks in light resistance, causing a problem that the color of the image fades with time.
When a dye having a relatively large molecular weight is used in order to avoid the above problem, the sublimation rate of the dye in the course of recording at a high speed is so low that no image having a satisfactory density can be provided.
The reproduction of a full-color image in the thermal transfer method using a thermal head relies upon subtraction color mixing. In this case, a combination of three primary colors of yellow, magenta, and cyan is very important for reproducing a satisfactory full-color image. In the case of conventional thermal transfer sheets using three color dyes, the dyes are satisfactory in one or two of color density, sharpness, and various types of fastness, particularly light fastness. However, a combination of three color dyes satisfying all the above requirements is not known in the art.
Accordingly, an object of the present invention is to provide a thermal transfer sheet for a thermal transfer system using a sublimable dye, which thermal transfer sheet can form a sharp full-color image having a satisfactory density and, at the same time, excellent various types of fastness, particularly excellent light fastness.